1. Field of the Invention
This invention relates to improvements in electrical circuitry for automatically establishing a reference output value of an analog circuit, particularly in phase locked loop circuits, or the like.
2. Relevant Background
In the operation of many circuits, circuit offsets are oftentimes compensated in quiescent circuit states to minimize their effects on the output signal. One way that this can be done, for example, is to measure the output of the circuit under quiescent conditions and adjust the circuit bias to achieve a desired output voltage, usually, but not necessarily, zero.
This initialization is many times a critical requirement for phase locked loop circuits that employ linear components. In such circuits, it is important to reduce the circuit offsets as much as possible, since such offsets are integrated by analog integrator circuit portions of the phase locked loop, thereby introducing steady state phase errors.
When circuit components are permanently adjusted to compensate for circuit offsets, oftentimes component aging and variations in circuit operating voltages change the output error compensation, deleteriously affecting the operation of the circuit. What is needed is a circuit that automatically adjusts the output of a circuit, such as a phase locked loop circuit or the like, that automatically initializes the circuit to a quiescent value, such as zero or other value, and that can operate automatically in response to a condition, such as a power-on event, or the like.